This invention relates to cam-operated dishwasher controls used to provide a timed water fill.
In prior art dishwasher controls, water fill duration is controlled by a cam-operated switch lifting to begin or end a water fill cycle. When the cam-operated switch lifts to control fill duration, lifting of the cam-operated switch requires a cam-follower to ride up a ramp to make contact. The distance the camstack must rotate for the cam follower to ride up the ramp to make contact is called the contact air gap. The contact air gap requires time to traverse resulting in the introduction of a major variable that causes water fill duration to be inaccurate.
Some prior art dishwasher controls use a constant motion drive system to advance the camstack which results in switch actuation rates that are relatively slow. The slow switch actuation rates, acting during the contact air gap, causes fill duration time to vary approximately .+-.10% with a constant motion drive. Poor fill tolerance permits excessive water usage, excessive heating element power consumption to heat the extra water, and additional wasted power provided to other components such as the water valve and timer motor over the life of the appliance.
To achieve higher fill accuracy, some prior art dishwasher controls use a variable speed camstack advance feature that increases camstack advance speed during fill switching. The faster switching rates achieved in a variable speed dishwasher control decrease the time required to traverse the contact air gap resulting in a fill tolerance within .+-.2% to 4% of the desired fill duration. But variable speed camstack advance dishwasher controls have the disadvantages of greater cost, greater complexity, decreased reliability, noisier operation, and rougher operator feel.
Another method prior art dishwasher controls have used to increase fill accuracy is to employ drop actuated switches that do not have a contact air gap to traverse and switch almost instantaneously. But in prior art drop actuated switch controls this method has required a separate cam and switch for each function and position desired to be controlled. For instance using this method in a dishwasher control to turn a motor "on" and "off" and turn a water valve "on" and "off" would require four cams and four cam-operated switches. Although this method eliminates the need to traverse a contact air gap, the additional cams and cam-operated switches increase the accumulation of mechanical tolerances which also decreases water fill accuracy.
The recent focus on reducing energy consumption of appliances, along with the Department of Energy dishwasher energy consumption standards to be implemented in 1994, has created the need for a dishwasher cam-operated control that achieves high accuracy water fill control. Although variable speed cam-operated dishwasher controls have good fill accuracy, their undesirable characteristics include greater cost, greater complexity, decreased reliability, often noisy operation, and often rough operator feel. What is desired is a constant speed cam-operated dishwasher control with the attributes of low cost, simplicity, reliability, quiet operation, and smooth operator feel that also achieves high accuracy fill control.